1. Field of the Invention
The present invention relates to a method and apparatus for measuring the sizes of particles in a falling state. The method and apparatus according to the present invention is used, for example, for measuring the size of iron ore or coke falling into a blast furnace in the iron industry.
2. Description of the Related Art
It is often necessary to continuously measure the sizes of particles which are in the falling state when being supplied into a vessel or the like.
In the operation of a blast furnace in the iron industry, materials such as iron ore and coke are accumulated in a charging hopper at the top of the blast furnace and are caused to fall intermittently into the blast furnace.
The thus falling materials have a great influence on the flow of gas in the blast furnace, which is a very important factor in maintaining a stable and efficient operation of the blast furnace, depending on the sizes of the particles of the materials. Also, segregation of the particle materials is often carried out while the particle materials are being transferred by a conveyor or the particle materials are going down through the charging hopper, depending on the sizes of particles of the particle materials. For these reasons, it is necessary to measure the sizes of particles of the particle materials immediately before the particle materials are charged into the blast furnace.
In the prior art, however, sizing of the particles has been carried out only by taking a certain amount of the particles as a sample from the particles which are being transferred by a conveyor and measuring the sizes of the sampled particles by a screen. A steady and continuous measurement technique for measuring the sizes of particles has not been established.
A method for measuring the sizes of minute particles such as those having a size of less than several hundred micro-meters in the falling state by using the diffraction of a laser light is disclosed in the Transactions of Japanese Mechanical Engineers Society, Vol 49, No. 442, Pages 2.30 to 2.38, June, 1983. However, this method cannot be applied to particle materials which are being charged into the blast furnace in a large amount, such as several hundred kilograms per second, wherein the particles have a size of several millimeters to several tens of millimeters and are falling within a cylinder having a diameter of several tens of centimeters, which does not permit the transmission of laser light.